By government edict, motor vehicle manufacturers are being required to provide passive passenger restraint systems, either seat belts or air bags, capable of holding vehicle occupants safely in their seats under adverse conditions, such as during a collision of the vehicle with a stationary object or another vehicle. As applied to seat belt systems, a passive system is one in which a shoulder harness, a lap belt, or a combination of both, automatically wrap around a seat occupant, for example, on the closing of the vehicle door adjacent the occupied seat.
In its simplest acceptable form, as utilized by a leading manufacturer of small vehicles, the passive seat belt system comprises a two-point system in which a shoulder harness is attached at one end to the vehicle door adjacent one side of the seat, and at its other end to the vehicle floor at the other side of the seat. When the vehicle door is opened, the harness swings away from the seat, and when the vehicle door is closed, the harness diagonally embraces the seat and the body of any passenger seated therein. Reference may be made to U.S. Pat. No. 3,931,988 issued Jan. 13, 1976 to Klaus Oehm et al for a "Vehicle Safety Device" for such a passive restraint system. As noted in this patent, the opening and closing movement of the door requires protraction and retraction of the shoulder harness. Accordingly, the latter is coupled to a take-up reel capable of unwinding as the door opens and winding as the door closes. A locking mechanism prevents the unwinding of the harness when an impact or sudden deceleration load is applied to the harness. See U.S. Pat. No. 3,946,965 issued Mar. 30, 1976 to H. Singh for a "Vehicle Sensitive Inertia Retractor" that exemplifies such a reel locking mechanism.
Even though a two-point system, as disclosed in U.S. Pat. No. 3,931,988, is considered acceptable in a passive restraint system, there are some individuals who do not feel they are fully protected without a lap belt as found in a conventional three-point harness lap belt system. Attempts to design a passive three-point system have as yet not been successful. The systems that are exemplified in the prior art are complicated and cumbersome and require a various assortment of pulleys, cables, links and springs in the mechanisms that are responsive to movement of the vehicle door to place the shoulder harness and lap belt segments in passenger restraining position.